This sounds like what happened to my truck. when you are holding the lever up in 2nd with the clutch and you let the clutch out (keeping pressure on lever upwards), does the lever go up then engage second gear correctly?
Mine did that and it turned out the clutch lever that goes into the tranny was pushing one of the shift rods out of second, so when the clutch was not depressed, it went in fine. So i adjusted the nut and the clutch lever and now no more problems.
I probably did that the wrong way but it works.
